Heretofore, a vehicle air conditioning apparatus has an air conditioning unit, including a centrifugal blower, a cooler unit and a heater unit. The centrifugal blower controls an amount of air blown into a passenger compartment. The cooler unit has a cooling heat exchanger, such as an evaporator, for cooling and dehumidifying air. The heater unit has a heating heat exchanger, such as a heater core, for heating air.
The air conditioning unit is generally installed at a front part in a passenger compartment of a vehicle and provided with an air conditioning case forming an air passage. The air conditioning case is attached to a fire wall (dash panel), disposed between an engine compartment and the passenger compartment. Therefore, while vibration of an engine, disposed inside the engine compartment, or vibration of the centrifugal blower is transmitted through the dash panel, a sidewall 102 of an air conditioning case 101 is vibrated so as to generate sounds. Accordingly, the sounds are likely to be uncomfortable for a passenger in the vehicle.
Particularly, such sounds are likely to be generated in a sidewall 102 shown in FIGS. 6A and 6B, which has a very large span to a connective portion for an adjoining unit case, and an air conditioning case 101 shown in FIG. 7, having a sidewall 102 in which adjoining reinforcing ribs are disposed at large intervals. Therefore, for example, outer reinforcing ribs 103 are integrally formed wholly on the sidewall 102 of the air conditioning case 101 with a grille shape, and a rectangular board 104 is adhered to the air conditioning case 101, thereby restricting the sidewall 102 of the air conditioning case 101 from being vibrated and keeping the silence. A length h shown in FIG. 7 indicates height of the outer reinforcing rib 103. Therefore, a vehicle air conditioning apparatus disclosed in JP-A-H11-62896 (Pages 1–4, FIGS. 1–4) is provided.
However, in the conventional vehicle air conditioning apparatus shown in FIGS. 6A, 6B and 7, the air conditioning case 101 is required to be enlarged, thereby occupying room in a front part of the passenger compartment. When the room occupied with the air conditioning unit in the front part of the vehicle is restricted, the cross-sectional area of the air passage formed inside the air conditioning case 101 is required to be downsized by the projected height of the outer reinforcing rib 103 or the board thickness of the rectangular board 104. Therefore, when the evaporator and the heater core are disposed be rectangular to the flowing direction of the air flowing inside the air passage formed inside the air conditioning case 101, i.e., to occlude the air passage, heat exchange area on the evaporator or that of the heater core is reduced. Accordingly, the air conditioning performance of the air conditioning unit drops.